1. Field of the Invention
The present invention relates to angular velocity/angular acceleration calculators, torque estimators, and combustion state estimators, and particularly relates to an angular velocity/angular acceleration calculator, a torque estimator, and a combustion state estimator for an internal combustion engine.
2. Description of the Background Art
Highly accurate control of an internal combustion engine is effectively realized by measuring a combustion state of the engine and controlling the engine with a measurement result thereof being fed back. For such highly accurate control, it is important to precisely measure the combustion state of the engine. The combustion state of the engine can be measured by measuring an internal pressure of a cylinder with a cylinder internal pressure sensor to calculate a torque, or by estimating a gas pressure torque according to a crank angle sensor signal.
Japanese Patent Application Laid-Open No. 2005-61371 discloses a method for estimating a gas pressure torque according to a crank angle sensor signal. In Japanese Patent Application Laid-Open No. 2005-61371, an average angular acceleration of a crankshaft in a predetermined crank angle range is obtained according to a crank angle measured with a crank angle sensor, and an average value of gas pressure torques is estimated according to the average angular acceleration, a previously obtained moment of inertia around the crankshaft, and a previously stored friction torque.
However, problems on durability and cost arise in such a method of measuring an internal pressure of a cylinder with a cylinder internal pressure sensor and calculating a torque. In the method disclosed in Japanese Patent Application Laid-Open No. 2005-61371, what is calculated is not an angular acceleration of the crankshaft but the average angular acceleration in the predetermined crank angle range. Thus, only estimated is an average value of gas pressure torques. Further, the method of Japanese Patent Application Laid-Open No. 2005-61371 is merely for obtaining an angular velocity according to a crank angle by difference approximation and calculating the average angular acceleration according to a difference in angular velocity between two predetermined crank angles. Therefore, this method is not for calculating an angular acceleration.
In the method disclosed in Japanese Patent Application Laid-Open No. 2005-61371, only the friction torque, which is a part of an external torque necessary for estimation of a gas pressure torque, is previously stored and used as a map on a rotational speed of an engine and a temperature of coolant water. Accordingly, the method of Japanese Patent Application Laid-Open No. 2005-61371 is limitedly applicable since a gas pressure torque can be measured only in a case where an external torque excluding a friction torque is obviously equal to zero or in a case where a load torque can be estimated with an additional measurement device such as an inclination sensor.